I have a 2001 supercrew with 5.4l i bought last night. has all new coil packs plugs and wires. Idle bounced from 850 to 1250 give or take. but i believed it to be tps and he said thats what garge said as well. well I got it home took old tps off to discover the end of throtle body shaft was bent and broke off. soo I went and bought new throtle body. it idle funny agian at first but know idles perfect after i re started idl if computer reset or something. It now only idles fun and surges when you turn a/c on it bounces up and down shut it off goes back down, when it kick up ac pump clutch spins, and when idles down it shuts off, but it did this b4 new tps also so im kinda lost in suggestions would be greatly apreciated. thanks James

 

When you changed the throttle body, did you clean or replace the IAC?

 

just cleaned It. Should i replace it? I have a used one off another truck but I could get new one if need be.

 

Mine does the same as well. Never have figured out why. I can actually feel it when cruising on the highway, the truck slightly slows for a second when the ac cycles without any throttle movement on my part, just the ac kicking on and off.
The IAC is supposed to pick up on the added restriction on the drivebelt and compensate for it but somewhere along the line the message is either not being sent or it being delayed.
I know the IAC is clean. It almost seems like an electrical strain. Starting to think my alternator is weak. My headlights dim when rolling the windows up and down and it also effects rpms if idling. Could a voltage drop from the pump kicking on cause that without the IAC picking up on it?

Didn't mean to hijack your thread. Thinking the issue may have something in common with yours and could help.

BTW, my ac is under extra strain being the system is a bit dry. I still after this long have not recharged my system since it was partially drained years ago.